1. Technical Field
This invention relates generally to sliding-type bearings, and more particularly to those having a powder metal bronze bearing material applied to a steel backing, such as used in engine bearings.
2. Related Art
It is common in engine bearing applications to bond a powder metal bronze alloy to a steel backing to journal a crankshaft or the like. The copper tin matrix provides a strong bearing surface that can withstand the loads subjected on the bearing in use. Such bearings must also exhibit suitable wear and seizure resistance properties, and for this purpose it is common to add a certain amount of lead to the bronze matrix which serves as a lubricant to the bearing surface. It is also common to add a flash coating of tin to the running surface to further enhance the wear and seizure characteristics of the bearing.
Due to environmental considerations, various substitutes for lead have been explored, but to date none have demonstrated the ability to truly substitute for lead without unduly sacrificing the strength, wear and seizure properties of engine bearings. It is an object of the present invention to provide a suitable lead-free bronze engine bearing that exhibits comparable or better properties than those containing lead.